See this recently asked question: Why can't I see a preview of a Word doc in the preview pane using Windows Explorer? Win 7 64bit (Always first search for similar issues addressed in the past).
However, I just tested this issue on Windows 7 Enterprise, Service Pack 1, without LibreOffice installed (work machine). If I select a LibreOffice spreadsheet (.ods) or a text document (.odt) in explorer, a preview for each is available in the preview pane (Organize >> Layout >> Preview Pane). Note that you do not get a preview as the icon in the main window - not for any file types.
The files have to have the correct filename extension - upon download my Windows initially gave them .zip extensions. You said your file was a calc file, but that it had an .odt extension. Perhaps your problem is the wrong filename extension for the file type, because this will stop it working.
Edit:
Well, you learn something new every day. After seeing your further comment, I checked a few other workstations, and found variations on this issue, including one that displays thumbnails for Powerpoint files only and just icons for everything else. Curious, I googled the issue and found this: http://social.technet.microsoft.com/Forums/windows/en-US/b4a1819e-16af-4e07-9c45-49920382ced3/no-thumbnail-preview-for-word-documents-or-folders?forum=w7itproui . Sure enough, when I saved new documents in MS Office with “save thumbnail” checked, I can now get thumbnails in the explorer details pane.
However, this still didn’t give me thumbnails of odf documents in the explorer detail pane until I actually installed LibreOffice. But after installing the latest LO 4.3.0.4 on Win 7 Enterprise 64-bit, I can now get thumbnails of odt and ods documents in the explorer details pane whether they were created in MS Office or LO.
All I can say is that there are a lot of internet hits relating to issues with windows explorer not displaying thumbnails for a variety of filetypes.
